This invention relates to heat exchangers, and more particularly, to charge air coolers for internal combustion engines and methods of making the same.
For any of a variety of reasons, internal combustion engine systems are experiencing an increase in the use of turbochargers or superchargers. As is well known, a turbocharger includes a turbine wheel that is driven by the exhaust gases from the engine and which in turn drives a rotary compressor. A supercharger includes a rotary compressor which is directly driven by the engine or by a motor which is ultimately powered by the engine.
In either case, the rotary compressor compresses combustion air prior to its admission to the combustion chambers of the internal combustion engine. When a turbocharger is used, the system recovers part of the waste energy that results when incompletely spent exhaust gases are permitted to expand without performing work. Both types of system provide for higher compression ratios than are obtainable by the geometry of the internal combustion engine itself and allow the combustion of greater quantities of fuel for any given operating condition to provide an increase in engine power.
It has long been observed that when the incoming combustion air is compressed by the rotary compressor, it is simultaneously heated which, in turn, means that its density is decreased. Thus, at any given pressure, a unit volume of hot air from a turbocharger or a supercharger contains a lesser quantity of oxygen available for combustion than would an identical volume of cold air at the same pressure. This factor, in turn, places a limitation on the amount of fuel that may be burned in any given operating cycle of an internal combustion engine, which in turn limits the output thereof. Consequently, particularly in vehicular applications, a so-called charge air cooler has been introduced between compressor stages or between the compressor side of the turbocharger or supercharger and the intake manifold (or equivalent) for the internal combustion engine. The hot, combustion air from the turbocharger or the supercharger, is passed through the charge air cooler to the engine. At the same time, ambient air is passed through the charge air cooler in a flow path isolated from the combustion air, but in heat exchange relation therewith. Cooling of the combustion air is obtained to increase the density of the combustion air to ultimately provide a greater quantity of oxygen per charge of air to the engine to support the combustion of a greater quantity of fuel, increasing the output of the engine.
Charge air coolers operate in relatively stressful environments. The temperature of the charge air upon admission to the charge air cooler is typically in the range of 400-500xc2x0 F. while the exterior of the charge air cooler is subjected to ambient temperatures. As a result, considerable thermal stresses may be present.
More specifically, typical charge air coolers include a plurality of generally parallel, spaced tubes with headers at opposite ends to form a core. Side pieces extend along the side of the core. Inasmuch as the charge air hot air flows through the tubes but does not contact the side pieces, the tubes tend to elongate whereas the side pieces do not. This problem has generally been solved through the use of slits extending through the side pieces to divide each side piece into two separate elements which may separate as the tubes elongate as a result of thermal expansion.
This solution has been successful in minimizing and/or eliminating failures at the tube-to-header joints. However, it does little for failures occurring elsewhere.
In other cases, particularly where extremely long tubes are employed, as for example, in radiators for locomotives, tube receiving ferules have been disposed in slots in the headers and an elastomer precision molded about each ferule to interconnect the ferules and the header. Tubes are introduced into the ferules and then soldered to the ferules. This results in a floating tube construction wherein the tubes and the ferules may move relative to the headers as a result of the pliant nature of the elastomer interconnecting the ferules and the headers. Again, this approach solves all problems at the tube-to-header joints but does not solve all the problems.
Specifically, conventional charge air coolers have opposed headers receiving the tubes, and tanks are applied to the headers on the sides thereof opposite from the tubes. Particularly at the inlet tank and header connection, where hot air from the rotary compressor of the turbocharger or supercharger is introduced, because of the greater surface area of the tank, it is more able to dissipate heat rejected to it from the incoming charge air than can the header. Since, in the usual case, the headers and the tanks are elongated, the fact that the tank is able is dissipate more heat than a header results in unequal thermal expansion in the direction of elongation of the two, resulting in failures at the header/tank connection. The present invention is directed to overcoming one or more of the above problems.
It is the principal object of the invention to provide a new and improved charge air cooler and method of making the same.
More specifically, it is an object of the invention to provide a new and improved charge air cooler construction wherein thermal expansion of the inlet header and tank are made nearly equal so as to eliminate stresses at the point where the two are joined to one another, as well as a method of making such a charge air cooler.
An exemplary embodiment achieves the foregoing object in a charge air cooler for use with an internal combustion engine that includes a pair of spaced headers. Spaced tube slots are located in each of the headers with the slots in one header being aligned with slots in the other header to receive the ends of corresponding tubes. A pair of tanks are provided, one for each header, and are metallurgically bonded to the corresponding header on one side thereof. A plurality of elongated tubes, one for each corresponding slot in the header, extend between the headers and have opposite ends received in corresponding slots in the associated headers. The tube ends pass through at least the inlet header into the corresponding tank and past the one side of the inlet header to which the tank is bonded. A fluid-type metallurgical bond is employed to secure the tube ends and the corresponding ones of the slots and fins are provided to extend between adjacent ones of the tubes and to be in heat exchange relation therewith. Tanks are provided with charge air inlets and charge air outlets as appropriate and a body of heat resistant elastomer is bonded to the side of the inlet header opposite the tubes in surrounding and contacting relation to the tube ends thereat while allowing fluid communication between the tube ends and the interior of the tank which is bonded to that header.
As a consequence, the header is insulated by the elastomer body and operates at a cooler temperature than would otherwise be the case, the cooler temperature being approximately the same as that at which the tank operates so that the two experience approximately equal thermal expansion, thereby eliminating thermal stresses at their interface.
The slots in the headers may or may not be surrounded by flanges and a body of elastomeric material may be provided, not only at the inlet header, but at the outlet header as well. Preferably, the elastomer is a silicone-based elastomer and is of a liquid type that cures at room temperature. In addition, the elastomer is preferably a flowable type so it may be cured in situ on the header to which it is applied.
It is contemplated that the headers may have edge flanges and that the body of elastomer extends along substantially the entire length of the header between the edge flanges.
According to the invention, there""s also provided a method of making a charge air cooler for an internal combustion engine. The method comprises the steps of:
(a) assembling a plurality of elongated tubes to two spaced headers, each having tube receiving slots, such that the ends of the tubes extend through at least one of the headers past one side thereof;
(b) forming fluid tight metallurgical bonds between the tubes and the headers;
(c) applying a curable elastomer to at least the one side of the one header to substantially cover the same while allowing the ends of the tubes to remain open;
(d) curing the elastomer;
(e) metallurgically bonding a tank to at least the one header on the one side thereof; and
(f) providing a charge air inlet in the tank.
According to a preferred embodiment of the invention, the elastomer is a flowable elastomer and step (c) is performed by flowing the elastomer onto the one side of the header. It is also contemplated that the elastomer be curable at room temperature, so that step (d) can be performed at room temperature. The invention also contemplates that the step of providing a charge air inlet be performed before the step of bonding the tanks to the headers and that the bonding steps be performed by welding or brazing.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.